This invention relates generally to improved apparatus for heating liquids to provide thermal energy for the heating of room spaces and other uses.
In some prior liquid heating devices, blowers have been used to obtain the desired supply of fuel and/or combustion air in an effort to achieve hotter combustion temperatures, more rapid and complete burning of the fuel or other objectives. If such a blower is connected to the inlet door of a combustion chamber or firebox, however, it produces a positive pressure within the firebox. Such pressure can result in outward leakage of hot gaseous combustion products around such a door and can cause a dangerous discharge of such products, if an operator inadvertently opens the door without first shutting off the blower. If the blower is connected to the end of a final outlet stack from such a firebox, so that it tends to establish a negative pressure at the firebox door, the dangerous leakage can be avoided. In either case, however, I have recognized that the blower contributes primarily to the movement of air or gaseous combustion products through the system and not to the transfer of thermal energy from such combustion products to the liquid in the tank. In fact the blower may speed up such movement and tend to remove the hot gaseous products, before there is an adequate opportunity to transfer their thermal energy to the liquid in the tank.
In prior liquid heating devices in which the desired heat is obtained by the burning of solid fuels such as wood or other chunk fuels, I have found that there can be problems of inefficient or inadequate combustion, both during the start-up of combustion after a fire is ignited and during the subsequent burning of a load of solid fuel. In cases where at least part of a firebox or combustion chamber wall is in direct contact with the liquid to be heated, as is the case in almost any wood-fired tank or boiler, the liquid around the outside of the firebox can have a cooling or chilling effect on the firebox wall temperature, thus interfering with the achievement of efficient flame combustion temperatures in the range of 1600 degrees to 2000 degrees F. (Fahrenheit). Below such temperatures, incomplete combustion occurs resulting in creosote and particulate formation, which immediately deposit upon the cool firebox wall. Wood-fired tanks or boilers are therefore often thought of as undesirable sources of thermal energy which contribute a high proportion of pollutants to the surrounding atmosphere and which do not even achieve a relatively efficient heat transfer to the liquid in such a tank or boiler, i.e. a transfer of relatively high percentages of the available thermal energy which is stored within the wood or other chunk fuel.
While the present invention involves a recognition and possible solution of these and other problems in connection with liquid heating tanks and boilers in general, as well as in connection with the heating of such tanks and boilers by the burning of solid or chunk fuels such as wood, cob corn, briquettes, etc., I have found that the features of this invention provide special advantages in the novel type of solid-fuel burning apparatus described and claimed in my prior patent application Ser. No. 325,766, filed Nov. 27, 1981 (now issued as U.S. Pat. No. 4,401,101), which was a continuation in part of application Ser. No. 211,778, filed Dec. 1, 1980, and abandoned. In such combination apparatus, a solid-fuel-burning firebox is completely immersed (except for an open firebox end provided with a firebox door) within a liquid heating and thermal storage tank of very large capacity such as 1,000 gallons or more, and with a constantly open venting means at the top of the tank to maintain the tank pressure above the liquid at a level no higher than the ambient atmospheric pressure. The prior device includes a stack for conveying gaseous combustion products from the firebox through the liquid within the tank to an exhaust opening outside the tank, and the prior combination includes blower means connected to the stack for drawing a supply of combustion air into the firebox and forcing the gaseous combustion products out through the stack outlet, after thermal energy has been transferred from the combustion process and its resulting products as effectively as possible to the tank liquid which surrounds the firebox and stack. Such apparatus is designed for the intermittent or successive burning of individual solid fuel loads. Once the burning of such solid fuel loads has brought the tank temperature close to the liquid boiling point at the ambient pressure which is constantly maintained at the top of the tank, the thermal energy of the heated liquid can be stored up to several days and used, as needed, for the heating of room spaces or other building areas, before another solid fuel load needs to be burned.